1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a thin film resistor; a bleeder resistance circuit using a thin film resistor; and to a semiconductor device having the bleeder resistance circuit.
2. Description of the Related Art
Conventionally, a resistor made from a semiconductor thin film such as polysilicon and a bleeder resistance circuit using the resistor are used in many cases, and a resistor and a bleeder resistance circuit, which are formed using a semiconductor thin film having a conductivity type of either an N-type or a P-type, have been known.
However, when stress is applied to the conventional thin film resistor, for example, when resin packaging is made, there is a problem in that a resistance value of the thin film resistor is varied. Also, in the case of the bleeder resistance circuit, there is a problem in that a voltage dividing ratio is often varied after the resin packaging.
The present invention has been made in view of the above, and an object of the present invention is therefore to provide a bleeder resistance circuit with high precision, in which an initial resistance value is kept after packaging and an accurate voltage dividing ratio can be kept in the case of the bleeder resistance circuit, and a semiconductor device with high precision using such a bleeder resistance circuit, for example, a semiconductor device such as a voltage detector or a voltage regulator.
To achieve the above object, means adopted in a semiconductor device of the present invention are as follows. A thin film resistor and a thin film resistor of a bleeder resistance circuit having a plurality of such thin film resistors are comprised of a P-type thin film resistor formed of an N-type semiconductor thin film. Also, the present invention is characterized in that a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor and thus variations in resistance values of the P-type thin film resistor and the N-type thin film resistor by a piezo effect, which are described below, are cancelled by each other. Further, the present invention is characterized in that the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction and thus an occupying area of the bleeder resistance circuit is reduced.
Hereinafter, variations in resistance values by the piezo effect and an influence on the bleeder resistance circuit will be described.
When the stress is applied to the thin film resistor, the resistance value of the thin film resistor is varied by a so-called piezo effect, and the resistance value of the P-type thin film resistor is varied in the direction opposite to a variation in the resistance value of the N-type thin film resistor. This is also confirmed by experiments of the present inventor(s). For example, the resistance value of the P-type thin film resistor is decreased and the resistance value of the N-type thin film resistor is increased. The direction of the variation is changed depending on the direction of the stress.
When the IC is packaged by a resin, the stress is produced. Thus, as described above, the resistance value of the thin film resistor is varied by the piezo effect. Although the bleeder resistance circuit is used for obtaining an accurate voltage dividing ratio, since the resistance values of the respective resistors are varied, the voltage dividing ratio is also varied.
The thin film resistor according to the present invention is composed of the P-type thin film resistor made from the P-type semiconductor thin film and the N-type thin film resistor made from the N-type semiconductor thin film. Thus, even if the stress is applied, a variation in the resistance value can be prevented. Also, a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor. Therefore, even if the stress is applied, variations in the resistance values of the respective resistors are cancelled and thus an accurate voltage dividing ratio can be kept. Further, the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction, and thus an occupying area of the bleeder resistance circuit can be reduced.
The thin film resistor of the semiconductor device according to the present invention is composed of the P-type thin film resistor made from the P-type semiconductor thin film and the N-type thin film resistor made from the N-type semiconductor thin film. Therefore, even if the stress is applied by resin packaging or the like, variations in the resistance values of the respective resistors are cancelled and thus an initial resistance value can be kept. Also, a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor. Thus, an accurate voltage dividing ratio can be kept. When such a bleeder resistance circuit is used, a semiconductor device with high precision, for example, a semiconductor device such as a voltage detector or a voltage regulator can be obtained. Further, the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction, and thus an occupying area of the bleeder resistance circuit can be reduced.